Digital Equalization for Optical Distortion in Volume Holographic Data Storage Systems

摘要

Page-oriented memories such as holographic data storage systems (HDSS) have been a topic of active research owing to their ability to provide high data rates and high storage densities. The benefits of high data rates and high densities in a HDSS can be attributed to the parallel page format of data and the ability to multiplex several pages in the same storage volume [1]. In order to maximize the density and data rate simultaneously, one would ideally like to make the data pages constructed by the spatial light modulator (SLM) as big as possible i.e., bearing as many pixels as possible. For a given pixel size, as the number of pixels increases, the page size increases and the increased field of view makes the edges and corners of the page susceptible to optical distortion during imaging. In another paper of ours [2], we discuss the modeling and simulation of data pages for holographic storage suffering from optical distortion and inter symbol interference. We show through systematic simulation that the percentage page usability in a HDSS can decrease by about 25-50% if the maximum distortion allowed (at the edge of the page) is 20-40% of a pixel width. We assume here that the chief source of aberration in the imaging of the data page from the SLM to the charge-coupled detector (CCD) is optical distortion. We also assume that SLM and CCD misalignment effects are negligible. In this paper, we investigate the performance of signal processing in order to compensate for optical distortions and thereby to improve the page usability in a HDSS. The improved page usability translates directly to storage density and data rate gains.